Airframe timestamping technique for point-to-point radio links

ABSTRACT

calculate a phase offset based on the counter offset, and correct a phase of the first transceiver.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.16/046,877 filed Jul. 26, 2018, and entitled “Airtime TimestampingTechnique for Point-To-Point Radio Links”, which claims the benefit ofU.S. Provisional Patent Application No. 62/537,378 filed Jul. 26, 2017,and entitled “Airtime Time Stamping Technique for Point-To-Point RadioLinks at the PHY Level of Airframe Data” which is incorporated byreference herein.

BACKGROUND 1. Field of the Invention(s)

The present invention(s) generally relate to wireless receivers. Moreparticularly, the invention(s) relate to systems and methods fordetermining time offsets and correcting phase between two devicescommunicating over a wireless channel.

2. Description of Related Art

A Radio Transparent Clock (R-TC) can be employed to deliver highlyaccurate time using the IEEE 1588 protocol over microwave links. TheRadio Transparent Clock accounts for the packet delay variation andasymmetry of microwave link. Both quantities are crucial for IEEE 1588timing accuracy but unfortunately also an inherent property of microwaveradio interfaces.

Current synchronization techniques are capable of transferring frequencysynchronization across the physical layers used to transport the data(electrical, optical or wireless) but to achieve phase synchronizationalgorithms like IEEE 1588v2 may be utilized. Unfortunately, the phasesynchronization process at the packet level, as recommended by IEEE1588v2, imposes several restrictions and complexities if used acrosswireless links.

SUMMARY OF THE INVENTION

An example method comprises receiving, at a first transceiver, a requestairframe from a second transceiver over a wireless link of a network,the request airframe including a first timestamp indicating a first timeTS1 that the request airframe was transmitted to the first transceiver,the first transceiver and the second transceiver including a first andsecond counters, respectively, timestamping a second time indicationindicating a second time TS2 that the request airframe was received,generating a respond airframe and including within the respond airframea third time indication indicating a third time TS3 that the respondairframe is to be transmitted to the second transceiver, transmittingthe respond airframe to the second transceiver, providing, by the firsttransceiver, a timestamp information request to the second transceiver,receiving a timestamp information response, from the second transceiver,in response to the timestamp information request, the timestampinformation response including a fourth time indication indicating afourth time TS4, calculating, by the first transceiver, a counter offsetusing the first time, second time, third time, and fourth time asfollows:

${{{counter}\mspace{14mu} {offset}} = \frac{\left( {{{TS}\; 1} + {{TS}\; 4} - {{TS}\; 3} - {{TS}\; 2}} \right)}{2}},$

calculating, by the first transceiver, a phase offset based on thecounter offset, and correcting, by the first transceiver, a phase of thefirst transceiver.

In various embodiments, the first and second counters are synchronizedwith each other before the counter offset is calculated. The firsttransceiver and the second transceiver may have synchronizedfrequencies. The first counter may be a PTP counter.

In some embodiments, the method further comprises determining asymmetry(ASY) in the wireless link and calculating the counter offset includes

$\frac{\left( {{{TS}\; 1} + {{TS}\; 4} - {{TS}\; 3} - {{TS}\; 2}} \right)}{2} \pm {\frac{Asy}{2}.}$

The first transceiver may generate and transmit the respond airframeimmediately after receiving the request airframe. The first transceivermay transmit the timestamp information request to the second transceiverat any time after the respond airframe is received.

The method may further comprise providing, by the second transceiver, atimestamp information request to the first transceiver, receiving atimestamp information response from the first transceiver, in responseto the timestamp information request, the timestamp information responseincluding at least the second time indication, calculating, by thesecond transceiver, a counter offset using the first time, second time,third time, and fourth time as follows:

${{{counter}\mspace{14mu} {offset}} = \frac{\left( {{{TS}\; 1} + {{TS}\; 4} - {{TS}\; 3} - {{TS}\; 2}} \right)}{2}},$

calculating, by the second transceiver, a phase offset based on thecounter offset, and correcting, by the second transceiver, a phase ofthe second transceiver. Calculating the phase offset by the firsttransceiver may not be synchronized with calculating the phase offset bythe second transceiver. The wireless link may be a microwave link.

Another example method includes generating, by a first transceiver, arequest airframe to be sent to a second transceiver over a wireless linkof a network, the request airframe including a first timestampindicating a first time TS1 that the request airframe is to betransmitted by the first transceiver, the first transceiver and thesecond transceiver including a first and second counters, respectively,transmitting the request airframe to the second transceiver, receiving arespond airframe from the second transceiver, the respond airframeincluding within the respond airframe a third time indication indicatinga third time TS3 that the respond airframe is to be transmitted to thefirst transceiver, determining a fourth time indication indicating afourth time TS4 that the respond airframe was received, providing, bythe first transceiver, a timestamp information request to the secondtransceiver, receiving a timestamp information response, from the secondtransceiver, in response to the timestamp information request, thetimestamp information response including a second time indicationindicating a second time TS2 that the request airframe was received bythe second transceiver, calculating, by the first transceiver, a counteroffset using the first time, second time, third time, and fourth time asfollows:

${{{counter}\mspace{14mu} {offset}} = \frac{\left( {{{TS}\; 1} + {{TS}\; 4} - {{TS}\; 3} - {{TS}\; 2}} \right)}{2}},$

calculating, by the first transceiver, a phase offset based on thecounter offset, and correcting, by the first transceiver, a phase of thefirst transceiver.

The first and second counters may be synchronized with each other beforethe counter offset is calculated. The first transceiver and the secondtransceiver may have synchronized frequencies. The first counter may bea PTP counter. The method may further comprise determining asymmetry(ASY) in the wireless link and calculating the counter offset includes

$\frac{\left( {{{TS}\; 1} + {{TS}\; 4} - {{TS}\; 3} - {{TS}\; 2}} \right)}{2} \pm {\frac{Asy}{2}.}$

The first transceiver may transmit the timestamp information request tothe second transceiver at any time after the respond airframe isreceived.

In various embodiments, the method may further comprise providing, bythe second transceiver, a timestamp information request to the firsttransceiver, providing a timestamp information response to the secondtransceiver, in response to the timestamp information request, thetimestamp information response including at least the third timeindication, calculating, by the second transceiver, a counter offsetusing the first time, second time, third time, and fourth time asfollows:

${{{counter}\mspace{14mu} {offset}} = \frac{\left( {{{TS}\; 1} + {{TS}\; 4} - {{TS}\; 3} - {{TS}\; 2}} \right)}{2}},$

calculating, by the second transceiver, a phase offset based on thecounter offset; and correcting, by the second transceiver, a phase ofthe second transceiver.

Calculating the phase offset by the first transceiver may not besynchronized with calculating the phase offset by the secondtransceiver.

An example system may comprise a first transceiver including memory anda processor, the first transceiver configured to: receive a requestairframe from a second transceiver over a wireless link of a network,the request airframe including a first timestamp indicating a first timeTS1 that the request airframe was transmitted to the first transceiver,the first transceiver and the second transceiver including a first andsecond counters, respectively, timestamp a second time indicationindicating a second time TS2 that the request airframe was received,generate a respond airframe and including within the respond airframe athird time indication indicating a third time TS3 that the respondairframe is to be transmitted to the second transceiver, transmit therespond airframe to the second transceiver, provide a timestampinformation request to the second transceiver, receive a timestampinformation response, from the second transceiver, in response to thetimestamp information request, the timestamp information responseincluding a fourth time indication indicating a fourth time TS4,calculate a counter offset using the first time, second time, thirdtime, and fourth time as follows:

${{{counter}\mspace{14mu} {offset}} = \frac{\left( {{{TS}\; 1} + {{TS}\; 4} - {{TS}\; 3} - {{TS}\; 2}} \right)}{2}},$

calculate a phase offset based on the counter offset, and correct aphase of the first transceiver.

Another example system may comprise a first transceiver including memoryand a processor, the first transceiver configured to: generate a requestairframe to be sent to a second transceiver over a wireless link of anetwork, the request airframe including a first timestamp indicating afirst time TS1 that the request airframe is to be transmitted by thefirst transceiver, the first transceiver and the second transceiverincluding a first and second counters, respectively, transmit therequest airframe to the second transceiver, receive a respond airframefrom the second transceiver, the respond airframe including within therespond airframe a third time indication indicating a third time TS3that the respond airframe is to be transmitted to the first transceiver,determine a fourth time indication indicating a fourth time TS4 that therespond airframe was received, provide a timestamp information requestto the second transceiver, receive a timestamp information response,from the second transceiver, in response to the timestamp informationrequest, the timestamp information response including a second timeindication indicating a second time TS2 that the request airframe wasreceived by the second transceiver, calculate a counter offset using thefirst time, second time, third time, and fourth time as follows:

${{{counter}\mspace{14mu} {offset}} = \frac{\left( {{{TS}\; 1} + {{TS}\; 4} - {{TS}\; 3} - {{TS}\; 2}} \right)}{2}},$

calculate a phase offset based on the counter offset, and correct aphase of the first transceiver.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example environment including transceiver radiofrequency units (RFU) in some embodiments.

FIG. 2 is an example air frame structure in some embodiments.

FIG. 3 depicts an environment including microwave link partners incommunication over microwave channel in some embodiments.

FIG. 4 depicts an example airframe exchange between a first transceiverand a second transceiver in some embodiments.

FIG. 5 depicts a data flow between the two transceivers in someembodiments.

FIG. 6 depicts an example transmitting radio frequency unit in someembodiments.

FIG. 7 is a block diagram of an example transceiver RFU in someembodiments.

FIG. 8 is an example diagram depicting a simplified Finite State Machine(FSM) as one of the possible implementations of the data exchangeprocess.

DETAILED DESCRIPTION OF THE INVENTION

Some embodiments described herein provide simple and accurate phase andfrequency synchronization across wireless links. Methods and systems aredescribed that detect phase variations across wireless links. Theproposed methodology may allow for the creation of a phase and frequencysynchronized wireless network.

Some embodiments described herein includes methods and techniques thatsimplify detection of phase variations over that described regardingIEEE 1588v2 and may, in some embodiments, improve the accuracy of thephase offset calculation. The phase offset calculation may be used forphase synchronization.

In some embodiments, a phase offset is calculated as a relativedifference between near-end and far-end units and is calculated on bothsides of the wireless link independently. In some embodiments, beforethe offset calculation is calculated, frequency synchronization iscompleted and a time protocol counter may be at the data link layer oneach side of the wireless link.

As discussed herein, the time protocol counter (e.g., precision timeprotocol (PTP)) on the data link layer on the near-end side of thewireless channel may be referred to as a “local time protocol counter”and the time protocol counter on the far-end side as a “remote timeprotocol counter.”

While embodiments described herein may refer to the IEEE 1588v2standard, it will be appreciated that embodiments described herein mayutilize many different standards and many different protocols. In someembodiments, examples will be described showing an improvement over theIEEE 1588 V2 standard. As discussed herein, various techniques may beutilized in place of or in addition to any number of different protocolsand standards (e.g., protocols and standards for frequencysynchronization).

Further, as discussed herein, a “unit” may refer to the whole systemconnecting to other systems either with wired or wireless links.

If there are any additional time protocol counter(s) (e.g., PTPcounters) on the unit (e.g., for timestamping Ethernet packets) thenmost or all of the time protocol counters (e.g., PTP counters) on eachunit may be synchronized with each other. In various embodiments, timeprotocol counter synchronization on the unit is done after frequencysynchronization process and before phase offset calculation process. Inone example, a local 1PPS signal may be used to synchronize local PTPcounters. It may not be relevant for some embodiments described hereinwhich time protocol counter is a source for time protocol countersynchronization. This can be system dependent and/or defined by higherlayer(s) of phase synchronization process. Further, initial phaseinformation and master-slave direction may not be relevant for thismethod/technique.

In some embodiments, higher layer(s) of the phase synchronizationprocess use the phase offset calculation of the particular wireless linkto transfer phase synchronization across this wireless link. Higherlayer(s) of the phase synchronization process may use the initial phaseinformation to properly perform phase synchronization relative to theinitial phase source. The higher layer(s) of the phase synchronizationprocess may be aware of master-slave direction, if needed, by clocktype. Direction change may be fast and simple as phase offsetcalculation may be simultaneously and independently available on eachside of the wireless link.

Examples of the method/technique may be capable of phase offsetcalculation across the data link layer used to handle blocks of datapacked into airframes (e.g., OSI layer 2). Airframes are used fortransferring blocks of data across wireless links. There is asignificant time variation between packets and how they are packed intoblocks of data of airframe. This is one of the reasons why phasesynchronization at the packet level does not perform as well for phasesynchronization across wireless links.

Different embodiments may include any number of the following advantagesover the 1588v.2 standard:

-   -   (1) Better precision and accuracy two sides of the        point-to-point wireless link (e.g., two microwave routers        connected by a microwave radio link) may have better time        synchronization precision and accuracy by using methods        described herein compared to timestamping of packets at the        packet level (e.g., Ethernet packets). Packet level time        synchronization on the prior art introduces additional        scattering error (additional latency variation) as well as        additional deviation error (additional asymmetrical latency)        because there is a significant variable processing delay before        packets can be packed into airframes.    -   (2) Additional statistical precision may be gained through        averaging repeated measurements. With averaging measurement,        variations may be reduced or minimized due to cross-clock-domain        synchronization between asynchronous clock domains.    -   (3) The method/technique described herein may be independent of        the PTP master-slave configuration. In various embodiments, both        sides of the wireless point-to-point link calculate their own        phase offset (e.g., near-end side calculates phase offset        compared to far-end while far-end calculates its own phase        offset compared to near-end). The absolute values of both        offsets may be the same to the extent of measurement errors        while one is a positive value and the other is negative value.        This phase offset may be provided to the upper layer on both        sides regardless of master-slave configuration. The upper layer        may utilize the calculated phase offset in order to provide        transport of phase synchronization. The upper layer may be aware        of master-slave configuration, if needed, by clock type.        Direction change of master-slave configuration may be fast and        simple as phase offset calculation may be simultaneously and        independently available on each side of the wireless link.        However, the method/technique itself (or implementation of the        method/technique) may be independent of master-slave        configuration, which may make it an easier and more robust        solution compared to solutions that depend on master-slave        configuration.    -   (4) Independent of packet fragmentation. Various embodiments        described herein may be independent of packet payload data        including PTP timing packets (for IEEE 1588v2). When two or more        point-to-point radio links are used in parallel from one point        to another, then packet fragmentation (e.g., link aggregation        like L1LA) may be used over these parallel links to optimize        data traffic. This packet fragmentation process does not need to        be PTP IEEE 1588v2 aware.    -   (5) Unaffected user data bandwidth. Some embodiments described        herein may utilize transfer of local timestamps and other        required synchronization data between both sides of the wireless        link to calculate the phase offset. While timestamps required        for calculation may be taken close to each other with regards to        time, the transfer of this timestamp information between both        sides may not be time limited. Simple handshake may be used for        this information exchange within the data space for control        information, which may be available in every airframe, which may        not affect user data bandwidth (user traffic).

FIG. 1 depicts an example environment 100 including transceiver radiofrequency units (RFU) 102 and 104 in some embodiments. The transceiverRFUs 102 and 104 depicted in FIG. 1 are in wirelessly communication witheach other. In various embodiments, the transceiver RFUs 102 and 104communicate over microwave radio frequencies although it will beappreciated that transceiver RFUs 102 and 104 may communicate over anyportion of the wireless spectrum (e.g., not limited to the microwavespectrum).

Further, although depicted as communicating directly to each other, eachof the transceiver RFUs 102 and 104 may communicate via a tower or anyother receivers, transmitters, and/or transceivers.

The transceiver RFU 102 includes a first transceiver, a waveguide 106,and an antenna 108. The transceiver RFU 104 includes a firsttransceiver, a waveguide 110, and an antenna 112.

In various embodiments, the transceivers RFUs 102 and 104 may correctfor offset and phase utilizing systems and methods discussed herein.

The transmission over a microwave path may be based on a continuoussynchronous transmission of air frames separated by a preamble. FIG. 2is an example air frame structure 200 in some embodiments. Such atransmission scheme may be called a Constant Bit Rate (CBR).

In some embodiments, every air frame starts with the preamble 202 whichmay be a sequence known to the receiver. In this example, the preamble202 is followed by an Air Frame Link Control field 204, which containscontrol information defining the air frame 200. In various embodiments,the preamble 202 and the air frame link control field 204 are followedby blocks of QAM (or QPSK) symbols, called transport blocks (TB)206-216. Transport blocks (e.g., transport blocks 206-216) may becontainers for user data (e.g., Ethernet packets, TDM Payload, or thelike) and other required control data (e.g., ACM, ATPC, AGC, controlloops, or the like) exchanged mutually by microwave modems.

The size of those containers may depend on the current Adaptive CodingModulation (ACM) state and on the configured framing choice. Adaptivecoding modulation allows dynamic change of modulation and FEC level toaccommodate for radio path fading which is typically due to weatherchanges on a transmission path. Benefits of ACM may include improvedspectrum efficiency and improved link availability, particularly inwireless (e.g., microwave) links.

One of the disadvantages of changing the modulation level is that thischanges the throughput of the wireless (e.g., microwave) link. Suchchange on the wireless path (or any wireless path segment) causessignificant delay variation at the packet level. In one example, highPDV and asymmetry if the changes can occur only in one direction.Transport blocks (e.g., N*QAM Symbols) may also be used as theprocessing units for FFT operation and for further frequency domainprocessing. While discussion herein is directed to microwavecommunication, it will be appreciated that at least some embodiments anddiscussions herein may be applied to any wireless (e.g., radio frequency(RF)) communication.

The following includes some (not necessarily all) reasons for thecomplexity of obtaining exact timing of received and transmitted packetsat the physical level of a radio interface:

-   -   The microwave radio interface operates on a transport block        level as a basic data unit.    -   The transport block(s) require many stages of frequency and time        domain processing before the payload can be decoded.    -   Varying throughput due to ACM activity.

FIG. 3 depicts an environment 300 including microwave link partners 302and 304 in communication over microwave channel in some embodiments. Themicrowave link partners 302 and 304 may be or include transceivers,receivers, or transmitters. In some embodiments, the microwave linkpartner 302 may receive data to be transmitted over PHY 306.

The PHY 306 may be an Ethernet PHY (e.g., the data to be transmitted maybe received over an ethernet cable). The PHY 306 may process andmodulate the data into air frames (or any format) and provide themodulated data to the classification and routing module 308.

In various embodiments, systems and methods described herein utilizereceiving and providing data over Ethernet cable using an EthernetPhysical Layer device (e.g., PHY 306). Packets and/or PTP packets may bereceived from a switch or router. In various embodiments, the PHY 306may perform a timestamp at data ingress of the transceiver and PHY 314may perform a timestamp at data (e.g., the airframe) egress. Similarly,the PHY 322 of the second microwave link partner 304 may timestamp whendata (e.g., the airframe) is received over the microwave channel. Invarious embodiments, the PHY 330 may perform another timestamp ategress.

The classification and routing module 308 may direct data to betransmitted to the data packet queuing module 310 while directing datareceived from the radio frequency PHY 314 to the PHY 306. The datapacket and queuing module 310 may control data flow (e.g., bufferingand/or assist in load balancing) and provide the data to the schedulingmodule 312 which prepares the modulated data to be transmitted over theradio frequency PHY 314. The radio frequency PHY 314 may transmit thedata to another microwave link partner (e.g., microwave link partner304) and receive data. In various embodiments, the radio frequency PHY314 communicates over a microwave spectrum.

It will be appreciated that the microwave link partner (e.g., 302) maydown convert data (e.g., data received by a gigabit Ethernet PHY) toenable wireless transmission. The transceiver may up or down covert thedata to be transmitted (e.g., to an intermediate frequency where furtherprocessing may occur and then to an RF frequency for transmission).Further, there may be elastic buffers to transfer or change the dataspeed to a lower seed. As a result, phase and offset are increasinglydifficult to determine between devices across a wireless channel.Further, the radio may change modulation (e.g., in real-time).

The microwave link partner 304 may receive data from over the microwavechannel by the radio frequency PHY 322 which may provide the receiveddata to the classification and routing module 328 for routing andclassification of the received data to the PHY 330. The PHY 330 mayprovide the data to another digital device via Ethernet. Similar to themicrowave link partner 304,

The PHY 330 of the microwave link partner 304 may be an ethernet PHY(e.g., the data to be transmitted may be received over an ethernetcable). The PHY 330 may process and modulate the data into air frames(or any format) and provide the modulated data to the classification androuting module 328. The classification and routing module 328 may directdata to be transmitted to the data packet queuing module 326. The datapacket and queuing module 326 may control data flow (e.g., bufferingand/or assist in load balancing) and provide the data to the schedulingmodule 324 which prepares the modulated data to be transmitted over theradio frequency PHY 322. The radio frequency PHY 322 may transmit thedata to another microwave link partner (e.g., microwave link partner302) and receive data. In various embodiments, the radio frequency PHY322 communicates over a microwave spectrum.

Both microwave link partners 302 and 304 may include phase lock loops(PLLs) 316 and 332, respectively, to assist in recovery of clock signalsusing data received from over the wireless channel as described herein.The microwave link partners 302 and 304 may include system clocks 318and 334, respectively, that may include different time domains.

Offset and phase synchronization module 320 may determine offset andphase synchronization for the microwave link partner 302 based ontimestamps of the microwave link partners 302 and 304 as discussedherein. Similarly, offset and phase synchronization module 320 maydetermine offset and phase synchronization for the microwave linkpartner 304 based on timestamps of the microwave link partners 302 and304 as discussed herein.

FIG. 4 is a flowchart 400 that depicts an example airframe exchangebetween a first transceiver 502 and a second transceiver 504 (e.g.,microwave link partners 302 and 304, respectively) in some embodiments.Airframes may be transferred in both directions between local and remotesides with a constant airframe period. In this example, the local sidewill be referred to as the first transceiver 502 and the remote sidewill be referred to as the second transceiver 504. Also in this example,the wireless channel is a microwave channel. FIG. 5 depicts a data flow500 between the two transceivers 502 and 504 in some embodiments.

Timestamping of the airframe may be an independent process for radioegress and ingress directions and the timestamps. In variousembodiments, timestamps may be related to airframes rather than to anyspecific data inside data blocks. This enables the possibility to havefixed latency from the point of timestamp in the near-end modem, overthe air, to the point of timestamp in the far-end modem.

Phase offset between local and remote PTP counters on both sides ofpoint-to-point wireless link may be calculated using four timestampsbased on two airframes. To collect all four timestamps, the timestampingprocess of two airframes may be followed by a data exchange process. Forthe discussion herein, these two airframes may be named “request” and“respond” airframes.

In various embodiments, all airframes, regardless of how we call them,are intact from the traffic data point of view. The additional “channel”inside the airframe for may be utilized this method/technique. It may bedesired that this channel takes as little additional bandwidth aspossible. In the best case, it can be zero additional bandwidth if anexisting channel can be re-used.

In step 402, the first transceiver 502 may mark an airframe as a requestairframe 506. It will be appreciated that this airframe may be a PTPairframe, a time protocol airframe, or any other airframe.

In step 404, the first transceiver 502 (e.g., the radio frequency PHY314) timestamps the request airframe as TS1 and transmits the requestairframe 506 from the local side to the second transceiver (e.g., to theremote side (Unit 2) also called transceiver 504) of the point-to-pointwireless link. In some embodiments, the first transceiver 502 determinesa time TS1 and does not send the timestamp along with the requestairframe 506.

In step 406, the second transceiver 504 determines the time and maydetermine the time that the request airframe was received (TS2) 508.

In step 408, the second transceiver 504 may become the responding sideand may respond to this request by creating and transmitting an airframe(e.g., the first possible airframe) in the opposite direction. Theresponding airframe may be termed a “respond airframe” 510. The secondtransceiver 504 may determine a third time (TS3) that the respondairframe was sent. The second transceiver 504 may provide an indicationof TS2 or TS3 within the respond airframe.

In step 410, the first transceiver 502 may receive the respond air frameand determine a time that the respond airframe was received as TS4 512.

In some embodiments, the respond airframe follows the request airframeas soon as possible in order to minimize or reduce errors introduced bywander frequency of the whole system. Wander frequency has a typicalclock period of 100 ms while worst case delay between the request andrespond airframes is only a few milliseconds but could be less.

The data exchange process may follow the timestamping process. In someembodiments, this may be the required process to calculate the phaseoffset, however, it is not time critical. This means that timestamps andother required synchronization data from the responding side may betransferred to the requesting side through several airframes. This maybe done within an existing channel built inside the airframe fortimestamping purposes. Using the same channel may not be a requirementbut it may be desired so that no additional bandwidth is used.

In step 412, one side (e.g., the first transceiver or the secondtransceiver) may request time or counter data 514 from the other side(e.g., the first transceiver 502 may request synchronization data 514from the second transceiver 504 or the second transceiver 504 mayrequest synchronization data from the first transceiver 502) in step414. The responding side may mark the airframes (e.g., as “data”airframes). The receiving side may provide time indications thatindicate times that the requesting side does not have. For example, thesecond transceiver may provide, within a response to the request, timeindication indicating when the request airframe was received (TS2)and/or a time that the respond airframe was sent (TS3). Similarly, thefirst transceiver may provide time indication indicating when therequest airframe was sent (TS1) and/or a time that the respond airframewas received (TS4).

In step 416, the requesting side may calculate the offset (e.g., usingthe offset and phase synchronization module 320 or 336). In variousembodiments, offset is calculated on the requesting side aftercollecting the timestamps and other required synchronization data:

${Offset} = {\frac{\left( {{{TS}\; 1} + {{TS}\; 4} - {{TS}\; 3} - {{TS}\; 2}} \right)}{2} \pm \frac{Asy}{2}}$

Any asymmetry on the round trip radio link path (marked as “Asy”)influences the calculation as seen from the formula. Asymmetry may bereduced, minimized, or eliminated with the possibility of characterizingand/or measuring each part in the radio link between both sides. If thisdata can be provided by hardware (HW), then no additional measurementsregarding asymmetry may be required.

Value(s) representing asymmetry may be introduced at the time ofestablishing the wireless link (e.g., preamble locking) while othervalue(s) (e.g., another part) may be introduced by having differentmodulations for radio egress and ingress directions of the selectedbandwidth.

Asymmetry may be calculated based on information from the modem abouttransmit and receive FIFOs. An FPGA may calculate the asymmetry.

In step 418, the requesting transceiver may correct phase based on theoffset (e.g., the Offset and phase synchronization module 320 or 336 maycorrect phase using the offset). In various embodiments, the calculatedphase offset information is a result at the physical layer and isfurther available to the higher layer. The higher layer may use thisphase offset information to transport the phase synchronization on thepacket level. The higher layer may also initiate the phase offsetcalculation process. There may be also the possibility that the higherlayer repeats this process in order to track any changes, especiallywhen modulations are changed.

FIG. 6 depicts an example transmitting radio frequency unit 602 in someembodiments. Although a transmitter is described in FIG. 6, it will beappreciated that all or parts of the transmitter of FIG. 6 may be a partof the first transceiver 602 as discussed herein. In some embodiments,the transmitting radio frequency unit expresses components and a logicalflow of transmitting information over a wireless channel. Anytransceiver including any functionality may be utilized in performingall or part of the systems and/or methods described herein.

The transmitting radio frequency unit 602 (e.g., radio link partner 302or radio link partner 304) may comprise a modem module 604, apredistortion module 606, an adaptive module 608, mixer modules 610, 624and 636, filter modules 612, 616, 626, 630 and 638, oscillator modules614 and 628, a phase adjuster 618, an automatic gain control (AGC)module 620, amplification/attenuation module 622, a power amplifier 632,a signal quality module 634, waveguide filter 648, and waveguide 650.

In some embodiments, the transceiver 602 includes a digital signalprocessor (e.g., DSP). The DSP is any processor configured to provideone or more signals to the modem module 604. The digital signalprocessor (DSP) may comprise a digital signal processor, or anotherdigital device, configured to receiving a source signal intended fortransmission and converting the source signal to corresponding in-phase(I) and quadrature (Q) signals. For instance, the DSP may be implementedusing a digital device (e.g., a device with a processor and memory).Instructions stored on the storage system may instruct the DSP toreceive an input signal from a communications network interface, convertthe input signal to corresponding the in-phase (I) and quadrature (Q)signals, and provide the corresponding in-phase (I) and quadrature (Q)signals.

The modem module 604 may be any modem configured to receive one or moresignals to be transmitted. The modem module 604, in one example, mayreceive an in-phase (I) and quadrature (Q) signals and provide thesignals to the predistortion module 606. The modem module 604 maycomprise a modem device, or another digital device. The modem module 604may be configured to receive in-phase (I) and quadrature (Q) signals andmodulate the in-phase (I) and quadrature (Q) signals to encode theinformation.

The predistortion module 606 may receive the signal from the modemmodule 604 and improve the linearity of the signal. In variousembodiments, the predistortion module 606 inversely models gain andphase characteristics and produces a signal that is more linear andreduces distortion. In one example, “inverse distortion” is introducedto cancel non-linearity. The predistortion module 606 may receive apredistortion control signal based on a comparison of a signal from thepower amplifier 632. In one example, the predistortion module 606 mayreceive a signal based on the power amplifier 632 in order to adddistortion to an input signal to the power amplifier 632 to cancel(e.g., non-linear) noise generated by the power amplifier 632.

The adaptive module 608 may provide the predistortion control signalbased on the sample from the signal quality module 634 described herein.The predistortion module 606 may provide the I and Q signals to themixer module 610.

The mixer module 610, filter module 612, and the oscillator module 614may represent an upconverter configured to upconvert the signals to anintermediate frequency signal. Similarly, the mixer module 624, filtermodule 626, and oscillator module 628 also may represent an upconverterconfigured to further upconvert the signal to an RF signal. Thoseskilled in the art will appreciate that there may be any number ofupconverters configured to upconvert the signals within the transceiverradio frequency unit 602.

The mixer modules 610 and 624 may comprise mixers configured to mix thesignal(s) provided by the modem with one or more other signals. Themixer modules 610 and 624 may comprise many different types of mixerswith many different electrical properties. In one example, the mixer 610mixes I and Q signals received from the predistortion module 606 withthe filtered oscillating signal from the filter module 612 and theoscillator module 614. In another example, the mixer module 624 mixes asignal received from the amplifier/attenuator module 622 with thefiltered oscillating signal from the filter module 626 and theoscillator module 628.

The filter modules 612, 616, 626, and 630 may comprise filtersconfigured to filter the signal. The filter modules 612, 616, 626, and630 may comprise many different types of filters (e.g., bandpass filter,low pass filter, high pass filter, or the like) with many differentelectrical properties. In one example, the filter module 612 may be aband pass filter configured to filter the oscillation signal (orcomponents of the signal) provided from the oscillator module 614.Similarly, filter modules 612, 616, 626, and 630 may filter signals (orcomponents of the signals) from the oscillator module 614, theoscillator module 628, the mixer module 610, or the mixer module 624,respectively.

The oscillator modules 614 and 628 may comprise oscillators configuredto provide an oscillating signal that may be used to upconvert thesignal. The oscillator modules 614 and 628 may comprise any kind ofoscillator with any different electrical properties. In one example, theoscillator module 614 provides an oscillating signal to the filtermodule 612. The oscillator module 628 may provide an oscillating signalto the filter module 626.

The oscillator modules 614 and 628, either individually or together, maybe local or remote. In one example, the oscillating module 614 and/orthe oscillating module 628 may be remotely located and configured toprovide an oscillating signal to one or more transmitting radiofrequency units. In some embodiments, a single oscillating module mayprovide an oscillating signal to both the mixer module 610 and 624,respectively (e.g., optionally via a filter). In one example, theoscillator signal from the oscillator module may be altered (e.g.,oscillation increased or decreased) and provided to a different part ofthe circuit.

The signal quality module 634 may be configured to generate a phasecontrol signal to control the phase of a processed signal. In oneexample, the signal quality module 634 receives the upconverted RFsignal from the power amplifier 632 and mixes the signal with thefiltered oscillator signal or the upconverted signal from the secondupconverter (e.g., mixer module 624, filter module 626, and oscillatormodule 628). The signal quality module 634 may filter the signal andcompare the filtered, mixed signal with a predetermined phase value togenerate a phase control signal based on the comparison.

The phase adjuster 618 may comprise a variable phase control circuitconfigured to increase or decrease the phase of the signal to betransmitted. The phase adjuster 618 may comprise any different type ofphase adjuster or phase shifter with different electrical properties. Inone example, the phase adjuster 618 increases or decreases the phase ofthe signal received from the filter module 616. The phase adjuster 618may adjust the phase of the signal based on the phase control signalfrom the signal quality module 634.

The phase adjuster 618 may include one or more components. For example,the phase adjuster 618 may comprise one or more phase control elements.

The AGC module 620 may comprise an automatic gain control (AGC) circuitconfigured to increase or decrease the gain of the signal received fromthe phase adjuster 618. The AGC module 620 may comprise many differenttypes of AGCs with many different electrical properties. In one example,the AGC module 620 increases or decreases the gain of the signalreceived from the phase adjuster 618. The AGC module 620 may adjust thegain of the signal based on the gain control signal.

In various embodiments, in order to adjust the phase of the signal orthe amplitude of the signal, the signal quality module 634 may providecontrol signals to adjust the in-phase (I) and quadrature (Q) signals toachieve a desired adjustment. For example, in order to adjust the phaseor amplitude of the signal, the signal quality module 634 may utilizethe digital signal DSP to adjust the in-phase (I) and quadrature (Q)signals provided to the modem module 604 to achieve the desiredadjustment based on the predetermined phase value and/or thepredetermined amplitude value. In another example, in some embodiments,the signal quality module 634 may utilize the modem module 604 to adjustthe in-phase (I) and quadrature (Q) signals provided to thepredistortion module 606.

The amplification/attenuation module 622 may comprise an amplifierand/or an attenuator configured to amplify and/or attenuate a signal.The amplification/attenuation module 622 may be any kind of amplifier(s)and/or attenuator(s). Further, the amplification/attenuation module 622may comprise amplifiers and/or attenuators with any kind of electricalproperties. The power amplifier 632 may amplify the signal to betransmitted. It will be appreciated that the power amplifier 632 may addnoise to the signal to be transmitted (e.g., nonlinear noise) which maybe dynamically canceled through the addition of distortion in the signalto be transmitted by the predistortion module 606.

In some embodiments, the amplifier/attenuator module 622 receives asignal from the AGC module 620. The amplifier/attenuator module 622 mayamplify or attenuate the signal. Further, the power amplifier 632 mayamplify power of the signal (or components of the signal) after thesignal has been upconverted by the mixer module 624, the filter module626, and the oscillator module 628. The power amplifier 632 may thenprovide the signal to the signal quality module 634 and/or the waveguidefilter 648.

The transceiver radio frequency unit 602 may comprise the waveguidefilter 648, the waveguide 650, and/or a diplexer. The waveguide filter648 may be any filter coupled to the waveguide 650 and configured tofilter the electromagnetic waves (e.g., remove noise). The waveguide 650may provide the signal to the antenna via a diplexer. The diplexer mayprovide the signal to the antenna. The waveguide 650 may be anywaveguide kind or type of waveguide.

In various embodiments, by utilizing open loop calibration, the totalphase and amplitude for the whole transmitter path may be calibratedfrom I and Q input to the output of the power amplifier 632. In someembodiments, by calibration and look-up tables, the phase and amplitudemay be accurately detected, controlled, and set at the Tx outputdirectly or through adjusting I and Q signals at the input. The phaseoffset calculation, as discussed herein, may be processed at the PHYlevel (as opposed to the packet level). With PHY level processing, atleast some systems and methods described utilize the block data level(block level) of the airframe, the symbol level of the airframe, or anycombination of both.

Blocks of data may be mapped by the modem into symbols to be transmittedby the radio and are de-mapped by the modem using symbols received fromthe radio. The start of the airframe may be timestamped locally eitherat the block level or at the symbol level. In various embodiments, bothsides of a wireless link timestamp the airframe in the same manner toprovide a symmetrical environment from the time point of view.

FIG. 7 is a block diagram 700 of an example transceiver RFU 702 in someembodiments. Although a receiver is described in FIG. 7, it will beappreciated that all or parts of the transmitter of FIG. 7 may be a partof the second transceiver 504 as discussed herein. In some embodiments,the receiving radio frequency unit 702 expresses components and alogical flow of transmitting information over a wireless channel. Anytransceiver including any functionality may be utilized in performingall or part of the systems and/or methods described herein.

Block diagram 700 comprises an antenna 704 and a diplexer 710 coupled tothe waveguide 706. The waveguide 706 may provide the signal from theantenna 704 to the diplexer 710 via a waveguide filter 708. The diplexer710 may provide the signal to the receiving radio frequency unit 702. Insome embodiments, the receiving radio frequency unit 702 may comprisethe waveguide 706, the waveguide filter 708, and/or the diplexer 710.

The waveguide 706 may be any waveguide kind or type of waveguide. Forexample, the waveguide 706 may be hollow or dielectric. In someembodiments, the waveguide 706 comprises a rectangular to circularwaveguide. The waveguide filter 708 may be any filter coupled to thewaveguide 706 and configured to filter the electromagnetic waves fromthe waveguide 706 (e.g., remove noise).

In various embodiments, the receiving radio frequency unit 702 isconfigured to receive a signal from the antenna 704 via the diplexer 710and adjust the phase of the received signal. The phase of the receivedsignal may be adjusted based on a comparison of the phase of the signaland a predetermined phase value. In some embodiments, the receivingradio frequency unit 702 may also be configured to adjust the gain ofthe received signal. In one example, the receiving radio frequency unit702 may adjust the gain of the received signal based on a comparison ofa gain of the received signal with a predetermined gain value.

The receiving radio frequency unit 702 may be any receiver including,but not limited to, a traditional heterodyne receiver with RXintermediate frequency (IF) output. Those skilled in the art willappreciate that multiple receiving radio frequency units may be used toreceive the same signal (e.g., signals containing the same informationprovided by a wireless communication source). Each receiving radiofrequency unit may adjust the phase of the received signal,respectively, based on the same predetermined phase value. Similarly,each receiving radio frequency unit may adjust the gain of the receivedsignal, respectively, based on the same gain value. As a result, thephase and gain of the signal from each receiving radio frequency unitmay be the same or substantially similar (e.g., the phase and gain ofthe signals may be identical). The signals may be subsequently combinedto strengthen the signal, increase dynamic range, and/or more accuratelyreproduce the information that was wirelessly transmitted.

The receiving radio frequency unit 702 may compriseamplification/attenuation modules and/or power amplifiers 712, 724, and738, filter modules 716, 720, 730, and 734 mixer modules 718 and 732,oscillator modules 722 and 736, phase control module 714, automatic gaincontrol modules 726, 740, and 742, and variable phase module 728.

The amplification/attenuation modules 712, 724, and 738 may comprise anamplifier and/or an attenuator configured to amplify and/or attenuate asignal. The amplification/attenuator modules 712, 724, and 738 may beany kind of amplifiers and/or attenuators. Further, theamplification/attenuator modules 712, 724, and 738 may each compriseamplifiers and/or attenuators with any kind of electrical properties.

In some embodiments, the amplifier/attenuator module 712 receives asignal via the antenna 704 and the diplexer 710. Theamplifier/attenuator module 712 may be a low noise amplifier configuredto amplify the signal (or components of the signal) before providing thesignal to the filter module 716 and the phase control module 714.Further, the amplifier/attenuator module 724 may attenuate the signal(or components of the signal) after the signal has been downconverted bythe mixer module 718, the filter module 720, and the oscillator module722. The amplifier/attenuator module 724 may then provide the signal tothe automatic gain control 726. The amplification/attenuator module 738may attenuate the signal (or components of the signal) after the signalhas been downconverted by the mixer 732, the filter module 734, and theoscillator module 736. The amplifier/attenuator module 738 may thenprovide the signal to the automatic gain control 740.

Those skilled in the art will appreciate that each of theamplifier/attenuator modules 712, 724, and 738 may be the same as one ormore other amplifier/attenuator modules. For example,amplifier/attenuator modules 712 and 724 may both be amplifiers sharingthe same electrical properties while amplifier/attenuator module 738 maybe an attenuator. In another example, amplifier/attenuator modules 712and 724 may both be amplifiers but have different electrical properties.

Each amplifier/attenuator module 712, 724, and 738 may include one ormore components. For example, the amplifier/attenuator module 712 maycomprise one or more amplifiers and/or attenuators.

The filter modules 716, 720, 730, and 734 may comprise filtersconfigured to filter the signal. The filter modules 716, 720, 730, and734 may comprise many different types of filters (e.g., bandpass filter,low pass filter, high pass filter, or the like) with many differentelectrical properties. In one example, the filter module 716 may be aband pass filter configured to filter the signal (or components of thesignal) received from the amplification/attenuation module 712 beforeproviding the signal to the mixer module 718. Similarly, filter modules720, 730, and 734 may filter signals (or components of the signals) fromthe oscillator module 722, the phase adjuster 728, and the oscillatormodule 736, respectively.

Those skilled in the art will appreciate that each of the filter modules716, 720, 730, and 734 may be the same as one or more other filtermodules. For example, filters module 716 and 720 may both be filterssharing the same electrical properties while filter module 730 may beanother kind of filter. In another example, filters module 716 and 720may both be filters of a similar type but have different electricalproperties.

Each filter modules 716, 720, 730, and 734 may include one or morecomponents. For example, the filter modules 716 may comprise one or morefilters.

The mixer modules 718 and 732 may comprise mixers configured to mix thesignal received from the antenna with one or more other signals. Themixer modules 718 and 732 may comprise many different types of mixerswith many different electrical properties. In one example, the mixer 718mixes a signal received from the filter module 716 with the filteredoscillating signal from the filter module 720 and the oscillator module722. In another example, the mixer module 732 mixes a signal receivedfrom the filter module 730 with the filtered oscillating signal from thefilter module 734 and the oscillator module 736.

Those skilled in the art will appreciate that each of the mixer modules718 and 732 may be the same as one or more other mixer modules. Forexample, mixer modules 718 and 732 may both be mixers sharing the sameelectrical properties or, alternately, the mixer modules 718 and 732 maybe another kind of mixer and/or with different electrical properties.

Each mixer modules 718 and 732 may include one or more components. Forexample, the mixer module 718 may comprise one or more mixers.

FIG. 8 is an example diagram depicting a simplified Finite State Machine(FSM) as one of the possible implementations of the data exchangeprocess. Note that timestamping of airframes is done in this examplewith regards to the state of the FSM and with regard to the receivedairframes.

Each side of wireless link may start its own process of phase offsetcalculation and that they may be independent between each other. Fromthe time point of view, they can start simultaneously or not. From thedata point of view, each side may collect its own timestamps forcalculating phase offset. It may not be relevant for thismethod/technique which side starts first.

The above-described functions and components can be comprised ofinstructions that are stored on a storage medium such as a computerreadable medium. The instructions can be retrieved and executed by aprocessor. Some examples of instructions are software, program code, andfirmware. Some examples of storage medium are memory devices, tape,disks, integrated circuits, and servers. The instructions areoperational when executed by the processor to direct the processor tooperate in accord with some embodiments. Those skilled in the art arefamiliar with instructions, processor(s), and storage medium.

Various embodiments are described herein as examples. It will beapparent to those skilled in the art that various modifications may bemade and other embodiments can be used without departing from thebroader scope of the present invention. Therefore, these and othervariations upon the exemplary embodiments are intended to be covered bythe present invention(s).

1. A method comprising: receiving, at a first transceiver, a requestairframe from a second transceiver over a wireless link of a network,the request airframe including a first time indication indicating afirst time TS1 that the request airframe was transmitted to the firsttransceiver, the first transceiver and the second transceiver includinga first and second counters, respectively; timestamping a second timeindication indicating a second time TS2 that the request airframe wasreceived; generating a respond airframe and including within the respondairframe a third time indication indicating a third time TS3 that therespond airframe is to be transmitted to the second transceiver;transmitting the respond airframe to the second transceiver; receiving,from the second transceiver, a fourth time indication indicating afourth time TS4; calculating, by the first transceiver, a counter offsetusing the first time, second time, third time, and fourth time asfollows:${{{counter}\mspace{14mu} {offset}} = \frac{\left( {{{TS}\; 1} + {{TS}\; 4} - {{TS}\; 3} - {{TS}\; 2}} \right)}{2}};$calculating, by the first transceiver, a phase offset based on thecounter offset, the calculating including determining asymmetry (ASY) inthe wireless link and applying the following:${{{phase}\mspace{14mu} {offset}} = {\frac{\left( {{{TS}\; 1} + {{TS}\; 4} - {{TS}\; 3} - {{TS}\; 2}} \right)}{2} \pm \frac{Asy}{2}}};$and correcting, by the first transceiver, a phase of the firsttransceiver.
 2. The method of claim 1, where the first and secondcounters are synchronized with each other before the counter offset iscalculated.
 3. The method of claim 2, wherein the first counter is aprecision time protocol counter.
 4. The method of claim 1, where thefirst transceiver and the second transceiver have synchronizedfrequencies.
 5. The method of claim 1, wherein the first transceivergenerates and transmits the respond airframe after receiving the requestairframe.
 6. The method of claim 1, wherein the first transceivertransmits the timestamp information request to the second transceiver atany time after the respond airframe is received.
 7. The method of claim1, further comprising: receiving from the first transceiver, at leastthe second time indication; calculating, by the second transceiver, acounter offset using the first time, second time, third time, and fourthtime as follows:${{{counter}\mspace{14mu} {offset}} = \frac{\left( {{{TS}\; 1} + {{TS}\; 4} - {{TS}\; 3} - {{TS}\; 2}} \right)}{2}};$calculating, by the second transceiver, a phase offset based on thecounter offset; and correcting, by the second transceiver, a phase ofthe second transceiver.
 8. The method of claim 7, where calculating thephase offset by the first transceiver is not synchronized withcalculating the phase offset by the second transceiver.
 9. The method ofclaim 1, wherein the wireless link is a microwave link.
 10. A methodcomprising: generating, by a first transceiver, a request airframe to besent to a second transceiver over a wireless link of a network, therequest airframe including a first time indication indicating a firsttime TS1 that the request airframe is to be transmitted by the firsttransceiver, the first transceiver and the second transceiver includinga first and second counters, respectively; transmitting the requestairframe to the second transceiver; receiving a respond airframe fromthe second transceiver, the respond airframe including within therespond airframe a third time indication indicating a third time TS3that the respond airframe is to be transmitted to the first transceiver;determining a fourth time indication indicating a fourth time TS4 thatthe respond airframe was received; receiving, from the secondtransceiver, a second time indication indicating a second time TS2 thatthe request airframe was received by the second transceiver;calculating, by the first transceiver, a counter offset using the firsttime, second time, third time, and fourth time as follows:${{{counter}\mspace{14mu} {offset}} = \frac{\left( {{{TS}\; 1} + {{TS}\; 4} - {{TS}\; 3} - {{TS}\; 2}} \right)}{2}};$calculating, by the first transceiver, a phase offset based on thecounter offset, the calculating including determining asymmetry (ASY) inthe wireless link and applying the following:${{{phase}\mspace{14mu} {offset}} = {\frac{\left( {{{TS}\; 1} + {{TS}\; 4} - {{TS}\; 3} - {{TS}\; 2}} \right)}{2} \pm \frac{Asy}{2}}};$and correcting, by the first transceiver, a phase of the firsttransceiver.
 11. The method of claim 10, where the first and secondcounters are synchronized with each other before the counter offset iscalculated.
 12. The method of claim 11, wherein the first, counter is aprecision time protocol counter.
 13. The method of claim 10, where thefirst transceiver and the second transceiver have synchronizedfrequencies.
 14. The method of claim 10, wherein the first transceivertransmits the timestamp information request to the second transceiver atany time after the respond airframe is received.
 15. The method of claim10, further comprising: providing to the second transceiver, at leastthe fourth time indication; calculating, by the second transceiver, acounter offset using the first time, second time, third time, and fourthtime as follows:${{{counter}\mspace{14mu} {offset}} = \frac{\left( {{{TS}\; 1} + {{TS}\; 4} - {{TS}\; 3} - {{TS}\; 2}} \right)}{2}};$calculating by the second transceiver, a phase offset based on thecounter offset; and correcting, by the second transceiver, a phase ofthe second transceiver.
 16. The method of claim 15, where calculatingthe phase offset by the first transceiver is not synchronized withcalculating the phase offset by the second transceiver.
 17. A systemcomprising: a first transceiver including memory and a processor, thefirst transceiver configured to: receive a request airframe from asecond transceiver over a wireless link of a network, the requestairframe including a first time indication indicating a first time TS1that the request airframe was transmitted to the first transceiver, thefirst transceiver and the second transceiver including a first andsecond counters, respectively; timestamp a second time indicationindicating a second time TS2 that the request airframe was received;generate a respond airframe and including within the respond airframe athird time indication indicating a third time TS3 that the respondairframe is to be transmitted to the second transceiver; transmit therespond airframe to the second transceiver; receive, from the secondtransceiver, a fourth time indication indicating a fourth time TS4;calculate a counter offset using the first time, second time, thirdtime, and fourth time as follows:${{{counter}\mspace{14mu} {offset}} = \frac{\left( {{{TS}\; 1} + {{TS}\; 4} - {{TS}\; 3} - {{TS}\; 2}} \right)}{2}};$calculate a phase offset based on the counter offset, the calculatingincluding determining asymmetry (ASY) in the wireless link and applyingthe following:${{{phase}\mspace{14mu} {offset}} = {\frac{\left( {{{TS}\; 1} + {{TS}\; 4} - {{TS}\; 3} - {{TS}\; 2}} \right)}{2} \pm \frac{Asy}{2}}};$ and correct a phase of the first transceiver.
 18. A system comprising:a first transceiver including memory and a processor, the firsttransceiver configured to: generate a request airframe to be sent to asecond transceiver over a wireless link of a network, the requestairframe including a first time indication indicating a first time TS1that the request airframe is to be transmitted by the first transceiver,the first transceiver and the second transceiver including a first andsecond counters, respectively; transmit the request airframe to thesecond transceiver; receive a respond airframe from the secondtransceiver, the respond airframe including within the respond airframea third time indication indicating a third time TS3 that the respondairframe is to be transmitted to the first transceiver; determine afourth time indication indicating a fourth time TS4 that the respondairframe was received; receive, from the second transceiver, a secondtime indication indicating a second time TS2 that the request airframewas received by the second transceiver; calculate a counter offset usingthe first time, second time, third time, and fourth time as follows:${{{counter}\mspace{14mu} {offset}} = \frac{\left( {{{TS}\; 1} + {{TS}\; 4} - {{TS}\; 3} - {{TS}\; 2}} \right)}{2}};$calculate a phase offset based on the counter offset, the calculatingincluding determining asymmetry (ASY) in the wireless link and applyingthe following:${{{phase}\mspace{14mu} {offset}} = {\frac{\left( {{{TS}\; 1} + {{TS}\; 4} - {{TS}\; 3} - {{TS}\; 2}} \right)}{2} \pm \frac{Asy}{2}}};$ and correct a phase of the first transceiver.